Show warning message when there are many/stale snappea tasks

As discussed in #11, there are scenarios (e.g. misconfiguration) where snappea
does not pick up the tasks. Events not showing up in Bugsink, w/o further
indication why that may be, leaves people confused. Better to warn explicitly
in that case.

bugsink/context_processors.py

@@ -1,27 +1,83 @@
 from datetime import timedelta
 
 from django.utils import timezone
+from django.utils.safestring import mark_safe
+
 from bugsink.app_settings import get_settings, CB_ANYBODY
+from bugsink.transaction import durable_atomic
+
+from snappea.settings import get_settings as get_snappea_settings
+from snappea.models import Task
 
 from phonehome.models import Installation
 
 
+FREE_VERSION_WARNING = mark_safe(
+    """This is the free version of Bugsink; usage is limited to a single user for local development only.
+    Using this software in production requires a
+    <a href="https://www.bugsink.com/#pricing" target="_blank" class="font-bold text-slate-800">paid licence</a>.""")
+
+
+def get_snappea_warnings():
+    # We warn in either of 2 cases, as documented per-case.
+
+    if get_snappea_settings().TASK_ALWAYS_EAGER:
+        # In TASK_ALWAYS_EAGER mode, there is no expectation that snappea runs, so there should be no warning either.
+        return []
+
+    with durable_atomic(using="snappea"):
+        task_count = Task.objects.all().count()
+        if task_count == 0:
+            # No tasks, no warnings.
+            return []
+
+        oldest_task_age = (timezone.now() - Task.objects.all().order_by('created_at').first().created_at).seconds
+
+    WARNING = (f"Snappea has {task_count} tasks in the queue, the oldest being {oldest_task_age}s old. It may be "
+               f"either overwhelmed, blocked, not running, or misconfigured.")
+
+    # 1. "a lot" of tasks in the backlog.
+    # We have a backlog because spikes are always to be expected, and dealing with them in a backlog is the feature that
+    # makes the server reliably able to handle them. So why would we warn about the backlog actually being used? Well,
+    # if there are "enough" (A.K.A. "a lot") of items in the backlog, you might be confused "why isn't this showing up?"
+    # 10s of confusion is a nice cut-off after which a banner should unconfuse you, and with 30 events per second (safe
+    # assumption given well-documented measurements) this is 300 events. Also: assumed to be rare enough to not
+    # over-warn.
+    if task_count > 300:
+        return [WARNING]
+
+    # 2. "a few", but _stale_ tasks in the backlog.
+    # If there are some (not a lot, but >0) items in the backlog, but they seem "stale", we warn too. Hard to come up
+    # with a precise definition of "stale", but we can say that if the oldest task is older than 5 seconds, people may
+    # start wondering why it's not happening. (whether that is being caused by backlogging or misconfiguration, in
+    # either case the warning is useful)". (An even better measure for low task_counts would be: if the last _picked-up_
+    # task is longer than some time ago, but we don't register picked-up time because we delete tasks in that case). For
+    # now, that's not complexity I'm willing to introduce, so we stick with the arbitrary 5s threshold.
+    if oldest_task_age > 5:
+        return [WARNING]
+
+    return []
+
+
 def useful_settings_processor(request):
+    # name is misnomer, but "who cares".
+
     installation = Installation.objects.get()
 
     nag_7 = installation.created_at < timezone.now() - timedelta(days=7)
     nag_30 = installation.created_at < timezone.now() - timedelta(days=30)
 
+    # (First version of "should I nag" logic): nag only after considerable time to play with the app, and for "some
+    # indication" that you're using this in production (the simplest such indication is that you've configured a
+    # BASE_URL that's not localhost). Subject to change.
+    system_warnings = [FREE_VERSION_WARNING] if nag_30 and '127.0.0.1' not in get_settings().BASE_URL else []
+
     return {
         # Note: no way to actually set the license key yet, so nagging always happens for now.
         'site_title': get_settings().SITE_TITLE + (" (non-production use)" if nag_7 else ""),
         'registration_enabled': get_settings().USER_REGISTRATION == CB_ANYBODY,
         'app_settings': get_settings(),
-
-        # (First version of "should I nag" logic): nag only after considerable time to play with the app, and for "some
-        # indication" that you're using this in production (the simplest such indication is that you've configured a
-        # BASE_URL that's not localhost). Subject to change.
-        'show_free_version_message': nag_30 and '127.0.0.1' not in get_settings().BASE_URL,
+        'system_warnings': system_warnings + get_snappea_warnings(),
     }
 
 

snappea/migrations/0003_task_created_at.py

@@ -0,0 +1,22 @@
+# Generated by Django 4.2.16 on 2024-11-15 10:42
+
+from django.db import migrations, models
+import django.utils.timezone
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("snappea", "0002_create_models"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="task",
+            name="created_at",
+            field=models.DateTimeField(
+                auto_now_add=True, default=django.utils.timezone.now
+            ),
+            preserve_default=False,
+        ),
+    ]

snappea/models.py

@@ -7,6 +7,7 @@ from . import thread_uuid
 
 
 class Task(models.Model):
+    created_at = models.DateTimeField(auto_now_add=True)
     task_name = models.CharField(max_length=255)
     args = models.TextField(null=False, default='[]')
     kwargs = models.TextField(null=False, default='{}')

theme/templates/base.html

@@ -44,13 +44,13 @@
                 </div>
             </div>
 
-            {% if show_free_version_message %}
+            {% for system_warning in system_warnings %}
             <div class="flex p-4 bg-yellow-100 border-b-2 border-yellow-200">
                 <div>
-                    This is the free version of Bugsink; usage is limited to a single user for local development only. Using this software in production requires a <a href="https://www.bugsink.com/#pricing" target="_blank" class="font-bold text-slate-800">paid licence</a>.
+                    {{ system_warning }}
                 </div>
             </div>
-            {% endif %}
+            {% endfor %}
 
             {% comment %} {# for use when we introduce a notification system #}
             <div class="flex p-4 bg-yellow-100 border-b-2 border-yellow-200">